Rubber compositions for tires comprise, in a known way, plasticising agents used for the preparation or synthesis of certain diene elastomers, for improving the processability of said compositions in the raw state and some of their use properties in the cured state, such as, for example, in the case of tire treads, their grip on wet ground or also their abrasion and cut resistance.
For a very long time, it has essentially been oils derived from petroleum and which are highly aromatic, known under the name of DAE (“Distillate Aromatic Extracts”) oils, which have been used to perform this function of plasticising agent. Many tire manufacturers are today, for environmental reasons, envisaging gradually replacing these DAE oils by substitute oils of the “non-aromatic” type, in particular by oils known as “MES” (“Medium Extracted Solvates”) or “TDAE” (“Treated Distillate Aromatic Extracts”) which are characterized by a very low level of polyaromatics (approximately 20 to 50 times less).
The Applicants have noted that the replacement, in tire rubber compositions, of DAE aromatic oils by these MES or TDAE oils is unexpectedly reflected by a reduction in the abrasion and cut resistance of said compositions, it being possible for this reduction to be even totally unacceptable in certain applications, in particular with regard to the problem of chipping of tire treads.
“Chipping” (or “scaling”) is a known damaging mechanism which corresponds to lamellar surface pieces, in the form of scales, being torn off from the constituent “rubber” (or rubber composition) of the treads under certain aggressive running conditions. This problem is encountered in particular with regard to tires for off-road vehicles or vehicles found on construction or civil engineering sites, which have to run over different types of soils, some of them stony and relatively aggressive; it has, for example, been described, along with some solutions for overcoming it, in the patent documents EP-A-0 030 579, FR-A-2 080 661 (or GB-A-1 343 487), or also in patent U.S. Pat. Nos. 3,927,144 and 4,968,764, which recommend, for overcoming it, the use of cyclopentadiene-based hydrocarbon resins.
On continuing their research, the Applicants have discovered that the replacement of a portion of these MES or TDAE oils by another specific plasticising agent makes it possible not only to solve the above problem but, which is even more surprising, to also improve the abrasion and cut resistance of the rubber compositions using conventional aromatic oils as plasticising agent.
Consequently, a first aspect of the invention is a rubber composition based on at least a diene elastomer, a reinforcing filler, a plasticising system and a crosslinking system, characterized in that said plasticising system comprises (phr=parts by weight per 100 parts of elastomer):                between 5 and 35 phr of an MES or TDAE oil;        between 5 and 35 phr of a C5 fraction/vinylaromatic copolymer resin.        
Another aspect of the invention is a process for preparing a rubber composition having an improved abrasion and cut resistance, this composition being based on a diene elastomer, a reinforcing filler, a plasticising system and a crosslinking system, said process comprising the following stages:                incorporating in a diene elastomer, during a first referred to as “non-productive” stage, at least a reinforcing filler and a plasticising system, by kneading thermomechanically the whole, in one or more goes, until a maximum temperature of between 110° C. and 190° C. is reached;        cooling the entire mixture to a temperature of less than 100° C.;        subsequently incorporating, during a second referred to as “productive” stage, the crosslinking system;        kneading everything until a maximum temperature of less than 110° C. is reached,and being characterized in that said plasticising system comprises:        between 5 and 35 phr of an MES or TDAE oil;        between 5 and 35 phr of a resin formed of C5 fraction/vinylaromatic copolymer.        
Another aspect of the invention relates, to a plasticising system which can be used for the plasticizing of a diene rubber composition, said system comprising, in combination, an MES or TDAE oil and a resin formed of C5 fraction/vinylaromatic copolymer, and to the use of such a system for the plasticizing of a diene rubber composition.
According to a preferred embodiment, the resin formed of C5 fraction/vinylaromatic copolymer comprises a weight fraction of cyclopentadiene and/or dicyclopentadiene which is less than 30%, which has proven to be favorable to the low-temperature hysteresis/high-temperature hysteresis compromise which a person skilled in the art of tires associates in a known way with the grip on wet ground and rolling resistance compromise.
Another aspect of the invention is the use of a composition according to the invention for the manufacture of a finished article or of a semi-finished product made of rubber intended for any motor vehicle ground-contact system, such as tire, internal safety support for a tire, wheel, rubber spring, elastomeric joint, other suspension element and vibration damper.
Another aspect of the invention is the use of a composition according to the invention for the manufacture of tires or semi-finished products made of rubber intended for these tires, these semi-finished products preferably being chosen from the group consisting of treads, crown reinforcing plies, sidewalls, carcass reinforcement plies, beads, protectors, underlayers, rubber blocks and other internal rubbers, in particular decoupling rubbers, intended to provide the bonding or the interface between the abovementioned regions of the tires.
Another aspect of the invention is the use of a composition according to the invention for the manufacture of a tire tread exhibiting in particular an improved cut and chipping resistance.
Another aspect of the invention is the finished articles and semi-finished products made of rubber themselves, in particular tires and semi-finished products for tires, when they comprise an elastomeric composition in accordance with the invention. The tires in accordance with the invention are intended in particular for passenger vehicles, such as two-wheel vehicles (motor cycles, bicycles), industrial vehicles chosen from vans, heavy-duty vehicles, i.e. subway, bus, heavy road transportation vehicles (trucks, tractors, trailers) or off-road vehicles, heavy agricultural vehicles or earthmoving equipment, planes, and other transportation or handling vehicles.
The invention and its advantages will be more easily understood in the light of the detailed description and of the exemplary embodiments which follow.